Browsing by Author "Rosas de Andraca, Fernando Ernesto"

Now showing 1 - 6 of 6
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    A low-complexity channel training method for efficient SVD beamforming over MIMO channels
    (2021) Kettlun, Felipe; Rosas de Andraca, Fernando Ernesto; Oberli Graf, Christian Robert
    Abstract Singular value decomposition (SVD) beamforming is an attractive tool for reducing the energy consumption of data transmissions in wireless sensor networks whose nodes are equipped with multiple antennas. However, this method is often not practical due to two important shortcomings: it requires channel state information at the transmitter and the computation of the SVD of the channel matrix is generally too complex. To deal with these issues, we propose a method for establishing an SVD beamforming link without requiring feedback of actual channel or SVD coefficients to the transmitter. Concretely, our method takes advantage of channel reciprocity and a power iteration algorithm (PIA) for determining the precoding and decoding singular vectors from received preamble sequences. A low-complexity version that performs no iterations is proposed and shown to have a signal-to-noise-ratio (SNR) loss within 1 dB of the bit error rate of SVD beamforming with least squares channel estimates. The low-complexity method significantly outperforms maximum ratio combining diversity and Alamouti coding. We also show that the computational cost of the proposed PIA-based method is less than the one of using the Golub–Reinsch algorithm for obtaining the SVD. The number of computations of the low-complexity version is an order of magnitude smaller than with Golub–Reinsch. This difference grows further with antenna array size.
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    Energy Efficient wireless communications
    (2012) Rosas de Andraca, Fernando Ernesto; Oberli Graf, Christian Robert; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    En los últimos años, la reducción de la energía necesaria para transferir información entre transmisor a receptor se ha constituido en un objetivo importante para las técnicas de comunicación inalámbricas. La búsqueda de nuevos métodos para aumentar la eficiencia energética de las comunicaciones inalámbricas se ha transformado en un activo campo de investigación. Algunos investigadores han sugerido que el uso de sistemas de múltiples antenas podría generar nuevas reducciones en el consumo energético de las comunicaciones inalámbricas. A pesar de un reciente interés en este tema, ningún análisis completo ha sido reportado sobre como el tamaño del arreglo de antenas, el tamaño de la modulación y la potencia irradiada han de elegirse para lograr comunicaciones energéticamente eficientes sobre canales con desvanecimiento.
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    Energy-efficient MIMO SVD communications
    (IEEE, 2012) Rosas de Andraca, Fernando Ernesto; Oberli Graf, Christian Robert
    Multiple-input multiple-output (MIMO) techniques can be used for reducing the energy consumption of wireless communications. Although some research has been reported on this topic, the rules by which the MIMO physical layer parameters should be chosen in order to achieve energy efficiency have not yet been formally established. In this paper, we analyze the case of MIMO singular value decomposition (SVD) technique. We present a model for the mean energy consumption of a MIMO SVD system per data bit transferred without error. We find that, for a given number of eigenchannels used with equal power allocation, exists a single optimal radiation power level at which the mean energy consumption is minimized. We also find that beamforming (only the best eigenchannel is used) is optimal in the energy consumption sense for long transmission distances, while the optimal number of eigenchannels to be used grows as transmission distance shortens. Using all the eigenchannels is optimal only for very short transmission distances.
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    Modulation Optimization for Achieving Energy Efficient Communications over Fading Channels
    (IEEE, 2012) Rosas de Andraca, Fernando Ernesto; Oberli Graf, Christian Robert
    It is commonly assumed that the energy consumption of wireless communications is minimized when low-order modulations such as BPSK are used. Nevertheless, the literature provides some evidence that low-order modulations are suboptimal for short transmission distances. A thorough analysis on how the modulation scheme and transmission power must be chosen as a function of distance in order to achieve energy-efficient communications over fading channels has not been reported yet. In this paper we provide this analysis by presenting a model that determines the energy consumed per payload bit transferred without error over correlated or uncorrelated random channels. We find that each modulation scheme has a single optimal signal- to-noise ratio (SNR) at which the energy consumption is minimized. We also find that if all modulations are operated at their optimal SNR, BPSK and QPSK are the optimal choices for long transmission distances, but as the transmission distance shortens the optimal modulation size grows to 16-QAM and even to 64- QAM. This result leads to showing that for short-range communications the lifetime of a typical low-power transceiver can be increased by up to 600% by selecting the optimal constellation rather than BPSK.
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    Nakagami-m approximations for MIMO SVD transmissions
    (IEEE, 2012) Rosas de Andraca, Fernando Ernesto; Oberli Graf, Christian Robert
    MIMO SVD modulation is an efficient way of sending data through a multi-antenna communication link in which the transmitter has knowledge of the channel state. Despite its importance, there is no simple formula available for its symbol error rate (SER) and therefore no intuitive characterization of the quality of this technique for data transmission. In this paper, we show that the statistics of each eigenchannel of MIMO SVD transmissions can be effectively approximated using the Nakagami-m fading model. We show that the SER of the entire MIMO SVD link can be approximated by the average of the SER of Nakagami-m channels. The expression found is simple and provides intuition about the quality of the channel for data transmission. We also establish upper and lower bounds for the SER of MIMO SVD, which allows us to estimate the diversity degree of the MIMO SVD transmission. Finally, we also present an approximation for the SER of MIMO SVD communications with channel coding.
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    Optimizing the code rate for achieving energy-efficient wireless communications
    (IEEE, 2014) Rosas de Andraca, Fernando Ernesto; Brante, G.; Souza, R. D.; Oberli Graf, Christian Robert
    Error correcting coding is a well-known technique for reducing the required signal-to-noise ratio (SNR) needed to attain a given bit error-rate. Nevertheless, this reduction comes at the cost of extra energy consumption introduced by the baseband processing required for encoding and decoding the data. No complete analysis of the trade-off between coding gain and baseband consumption of communications over wireless channels has been reported so far. In this paper, we study the energy-consumption of BCH codes with various code rates over AWGN and Rayleigh fading channels. Our results show that codes with low code rate are optimal for performing long-range communications, while is better to use less coding redundancy when the transmission distance is short. Our results also show that the transmission range of a low-power communication device can be increased up to 25% for AWGN channels and up to 300% for Rayleigh fading channels by using an optimized BCH code.